Heretofore, transparent polyurethanes have been made from high equivalent weight polyether intermediates and polyol curing agents, U.S. Pat. No. 3,755,262. However, such polyurethanes did not adequately function at elevated temperatures or have good outdoor environmental properties.
U.S. Pat. No. 3,866,242 to Slagel relates to a protective shield against bullets or missiles consisting of a polyurethane sheet of from 1/4" to 3/4" thick wherein the prepolymer is made from either a polyether polyol or a polyester polyol which is cured with an aromatic amine having a methylene bridge between two aromatic rings. Utilization of the amine curing agent does not result in a suitable transparent sheet inasmuch as an amber color is produced. The amber color darkens upon further exposure to light.